3V to 3.3V using D Cell Batteries Best Approach

[Veramacor]

I have a project that needs to run remotely and at times I need about 300 millamps for short periods.  Most of the time the project will run about 300 microamps.

I want to get the best battery life out of 2 standard D cell batteries, and my project has a need to run at 3.3V

Any suggestions on a step up regulator with an ultra low quiescent current?  I'm looking at about 700 microamp average current draw and would like to get about 2 years or so out of my batteries.

Thanks!

[AndyC_772]

It's not a trivial problem. Can you not use 3x C cells instead of 2x D cells, then use an ultra-low quiescent current linear regulator to drop the voltage down to 3.3V?

Failing that, I'd be looking long and hard at ways to make the circuit operate at a lower voltage. What is it that specifically requires 3.3V? Can the circuit not be modified to run at, say, 2.5V instead?

[grumpydoc]

my project has a need to run at 3.3V

I'd have thought most "3.3V" logic would run at 3V

2xD cell would be 3.2-3.3V fresh and lightly loaded anyway.

I'm looking at about 700 microamp average current draw and would like to get about 2 years or so out of my batteries.

Should be OK - if you have 12,000mAh alkaline D cells they will last 714 days (in theory).

Edit: Actually, this http://www.ti.com/lit/ds/symlink/tps61006.pdf might do you. 44µA quiescent and 80-90% efficient. Also something like a Duracell Ultra will probably give you 16-18,000mAh when lightly loaded so you should get your two years (just).

Nothing special about the above - just the first boost converter IC in Farnell's list designed for 3.3V output

[mariush]

Have a look at LT1308: http://www.linear.com/product/LT1308 

It has higher quiescent current at about 100 uA but it has a shutdown pin which takes it down to about 3 uA so if your IC uses so little power for long times it might be possible to do some tricks like charging a small capacitor/supercapacitor then running for minutes with the boost converter shut down and so on.
 

[Veramacor]

Wouldn't one advantage of a boost converter instead of a step-down regulator be that I could get 3.3V with drained batteries going as low as .7V (depending on boost converter)

It would seem that I could get more then 12,000 milliamp hours if that was the case assuming that 12,000 ma/h is for a D cell maintaining 1.5v.

I agree I wouldn't get much more, but I think I've seen a boost converter provide 200 milliamps at 3.3v with as low as a .7V input...

[Veramacor]

It's not a trivial problem. Can you not use 3x C cells instead of 2x D cells, then use an ultra-low quiescent current linear regulator to drop the voltage down to 3.3V?

Failing that, I'd be looking long and hard at ways to make the circuit operate at a lower voltage. What is it that specifically requires 3.3V? Can the circuit not be modified to run at, say, 2.5V instead?

The bottleneck in the project is a wifi module.  The ratings say absolute minimum voltage is 3.1V, but designed for 3.3V.  My PIC mcu can go down to 1.8V.  I could look into turning the WIFI off, but it's sleep mode is 5 microamps, meaning I can keep it 'on' for little current cost.  Turning it on may be troublesome, but that is a possibility,  Just running the micro at 1.8V and using a boost regulator to turn on and utilize 3.3v.  Very complex setup though

[lgbeno]

Check out TI TPS61200 very low Iq.

It's a boost converter that also has the capability to do down conversion so you can run your wifi module through the entire voltage range of 2 alkalines.

You may want to consider running you pic right off battery anyway to make the system more effiecnt then put the regulator to sleep when wifi is not on.

Just be careful because you cannot alway run the micro at max freq when using low voltage vin.

Tps61200 is a pretty neat part...

[Veramacor]

Check out TI TPS61200 very low Iq.

It's a boost converter that also has the capability to do down conversion so you can run your wifi module through the entire voltage range of 2 alkalines.

You may want to consider running you pic right off battery anyway to make the system more effiecnt then put the regulator to sleep when wifi is not on.

Just be careful because you cannot alway run the micro at max freq when using low voltage vin.

Tps61200 is a pretty neat part...

Thanks for the info.  I will check it out.  Sounds promising - thanks!